The Bishop of Lincoln and his wife kept many of their family papers, notebooks, and personal correspondence. In the case of Elizabeth Tomline, this was done deliberately for the benefit of her children and posterity. In one of her notebooks kept between October 29th and November 10th, 1801, she so much as directly states several times that she wants it to be preserved for the future. By the year 1801, she had been married to William Pitt's former tutor and personal friend George Pretyman, the Bishop of Lincoln, for 17 years. They had several children together, and they were by all accounts a devoted and well-suited couple.
Mrs Tomline had countless occasions from the 1780s onwards to come into contact with William Pitt in private life, so her testimony has an added credence.
One of the topics she alludes to in this notebook is whether or not Pretyman was ever a private secretary to Mr Pitt. For what it's worth, here's what she has to say. Apologies in advance for the numerous underlinings. I've tried to stay faithful to the original text.
I need hardly mention that all of these opinions are Mrs Tomline's own:
“…and here I shall observe that he [her husband, George Pretyman] was not actually Private Secretary (which office with the salary annexed to it was given to Mr Bellingham now Sir James [sic] Bellingham, at the request of Lord Chatham [Pitt's older brother]). He [her husband] was never considered as such by Mr Pitt’s family, and never received, or made any pecuniary advantage arising from his situation in any way whatever. This connection originated in the friendships which itself originated in the former connection of Tutor and Pupil. Mr Pitt was scarcely acquainted with the Secretary [Bellingham] he had appointed to oblige his Brother…" 
In a future post, I intend to contest this point - and argue that the Bishop of Lincoln did reap some pecuniary rewards via Pitt - with some evidence I've gathered from Pitt's accounts of the 1780s now held at The National Archives . Pitt made several payments to George Pretyman between 1782 and 1784, and the one which stood out the most to me was a transaction on July 20, 1784 from Pitt to Pretyman in the amount of £1,550!  More on that later.
Mrs Tomline goes on to state how she originally became acquainted with William Pitt:
“I became the confidential friend of Mr Pitt’s Sister Lady Harriot (whose idea at first was that “I must be good for something, or Dr. Pretyman would not have married me”) and with Mr Pitt’s knowledge my secrecy & discretion were wholly trusted.” 
On the passing of Edward James Eliot, arguably Pitt's closest friend and brother in-law, Mrs Tomline laments:
“...He [Eliot] died in 1797. In him Mr Pitt sustained a loss irreparable both on public and on private grounds. He [Pitt] felt it deeply. Alas! Its consequences are to be deplored indeed. Who are the persons that have since surrounded Mr Pitt? - Mr Pitt! whose noble disdain of suspicion, and aptitude to trust in the appearance of virtue if combined with pleasant manners, approaches to credulity notwithstanding all he had seen of this bad world. A rare example of purity & simplicity of heart united with transcendent Talents, and preserved in a situation of all others the most likely to corrupt it! That Mr Pitt is too easily persuaded by persons who seek their own honour & advantage even at the expense of his, is too true. But those who attribute this wholly to the influence of Flattery do not sufficiently understand his character…but I will own it is much more owing to the extreme easiness and kindness of Mr Pitt’s Temper…” 
Below are other wonderful anecdotes Mrs Tomline relates on the character and life of Pitt:
“…His own interest indeed, never in any occasion seems to occur to him. The vivacity of Mr Pitt’s disposition naturally led him to be fond of Company from Childhood; and he has ever sought relaxation from “the weighty business of the State” in the freedom of Social Converse with a set of private friends. He is extremely fond of Conversation - of lively, playful Conversation, and excels in it beyond all men. The pleasures of Conversation, and the pleasures of the Country, - not hunting & shooting [actually Pitt was fond of shooting], but improvements in His Grounds, riding & walking…and Reading (for he read almost everything worth reading), while in Office. - At Putney, and far a long time at Holwood, after a very moderate time at dinner, Mr Pitt & each of his friends used to take a Book, or stroll out as they were inclined, till business (to which two or three hours in the Evening was always devoted) or supper summoned them; and they always retired early (about eleven) to bed. - In Downing Street where I certainly saw Mr Pitt during Lady Harriot’s life time, he used generally to come up from dinner in to his Sister’s Apartment for an hour, or 1/2 an hour’s “lounge” with her, to whom he was attached with a degree of affection a character so like his own could alone deserve. I used to tell her ’twas pity she was his Sister, for no other woman in the World was suited to be his wife” . This last sentence is often quoted in biographies of Pitt, seemingly to illustrate how no woman was apparently suited to being married to Pitt.
On Pitt's working habits in his early days of public life, and how this changed as time went on, Mrs Tomline says:
"...At Wimbledon, the Evenings were usually spent in business - honourable to his [Pitt's] private as to his public character - “…But when most of his first set of friends were gradually withdrawn from this direct daily intercourse, by marriage, employments, and not from diminution of regard, new friends were naturally called in to make up their loss within his social circle. - New habits were acquired, and various circumstances unhappily [oe] to foster rather than annul them. Alas my heart bleeds when I think upon this subject.” 
By the tone of the above, I gather she didn't have a high opinion of Henry Dundas (Lord Melville), amongst others.
On a sombre note, Mrs Tomline devotes a few pages to Pitt's increasing dependancy on alcohol, particularly from the late 1790s, but probably even before that time:
"The Bishop [of Lincoln] never in his life saw Mr Pitt in the least affected by wine till the year 1798, when they were alone together one Evening at Holwood. Mr Pitt was at this time very unwell [this can be dated to June 1798 as after his duel with Tierney at the end of May, Pitt was very unwell and spent a great deal of time at Holwood] and in the earnestness of Conversation he [Pitt] filled his Glass so often as to affect his voice and manner, but not his understanding. The Bishop was excessively hurt and proposed his retiring to bed, to which he readily assented. This was the first time, but I cannot add it was the last in which the Bishop has had the poignant grief of observing similar circumstances. Alas! in other Society I fear - but I forbear. - With respect to the quantity of wine which Mr Pitt has drank from early youth, which has I believe astonished many, and given rise to many false aspersions, it was prescribed for him as a medicine by Dr. Addington to drink a bottle of port wine a day when he was a boy of fourteen, and this he did do under his Tutor’s eye in the course of the day, and as a task, rather than with any wish to exceed. Mr Pitt’s constitution was remarkably delicate at an early period of life. At fourteen he weighed only six stone & two p[oun]ds [that's 86 lbs in imperial weight!]. His Father, Lord Chatham, had the Gout while he was at Eton School, and the Constitutions of his Children were all thought to require a very full diet, and a great deal of port wine, and they were accordingly accustomed to this from Childhood….when motives of health originally induced the habit of drinking an unusual quantity, and till within a few years Mr Pitt had no inclination to exceed the limits of Temperance, nor did he exceed, except perhaps in Company which led him to excess. His moderation was remarked at White’s as a part of his singular character considering his uncommon vivacity…One of my authorities for these aspersions is Mr Eliot, himself a member of White’s and living much with Mr Pitt before he married his Sister as well as afterwards…” 
This last passage is particularly distressing as Pitt originally began drinking port every day on doctor's orders, and increasingly came to depend on it as the pressures of business and social convivality demanded it. Eventually, it became habit, and - it must be admitted - alcoholism. One must remember that those were different times. It must have been extremely upsetting for Pitt's friends to see him come to depend on alcohol to function, and to notice the visible signs it began manifesting on his physical health.
Although some of the passages quoted above have been reproduced elsewhere, as have other disparaging passages Mrs Tomline writes about Pitt's friend Henry Addington later in the notebook which I have not included here, it gives an insight into an outsider's perspective of Pitt's personality, and thus has a semblance of credibility.
1. The Kent History & Library Centre, Maidstone. Stanhope of Chevening Manuscripts, Pitt MSS: U1590/S5/C41. Notebook kept by Mrs. Tomline, October - November 1801.
2. The National Archives. Chatham Papers: PRO 30/8/219, Part 1. William Pitt's personal accounts between 1782-1788.
4. The Kent History & Library Centre, Maidstone. Stanhope of Chevening Manuscripts, Pitt MSS: U1590/S5/C41. Notebook kept by Mrs. Tomline, October - November 1801.