So I acquired a Canon MP700 all in one photo printer and the display reads "waste ink tank near full".

Now obviously I really don't want to take this to Canon service as this will cost a bomb.

I'm having difficulties finding the service manual for this model.
So if anyone has any tips or advice, or even a link for the service manual that would be great.

Where did you buy it? If you purchased a refurbished model or scored it from a friend or Joe you may need to reset/clear it.

MP700
Resetting the Waste Ink Volume Counter
1) Enter SERVICE MODE.---
By pressing [Menu] then [Copy] then [#]
2) Select TEST MODE. (using + or - keys)
3) Press the [OK] key.
3) Press the [8] key. (TEST MODE)
4) Press the [3] key.
5) Press the [0] key. (INK COUNT).
6) Press the [OK] key.
7) Press the [Stop/Reset] key
9) Press the [ON/OFF]

Good Luck and God Bless.

Computertech certainly has the go around code for you there, and that will work for a short time. However, you run the risk of clogging the purge unit and may even experience leaking out of the printer if allowed to go on for long. There is no "Tank" per se in these machines they are 3-4 layers of sponges at the bottom of the machine. The "Waste tank full" message comes when these sponges are at a heavy saturation point.
It is an easy fix if you are mechanically inclined. Simply remove the covers. There is 2 screws holding the internal workings of the machine to the bottom base. Once these screws are removed you should be able to lift the entire unit out from the base. There you will see the saturated sponges. Simply remove them and clean them with soapy water, wringing and rinsing as you go it will take awhile to remove the majority of ink. One you are satisfied you have gotten most of the ink out of th sponges, let them dry a day or possibly two. Reinstall the dry sponges and put the machine back together. Then perform the reset code offered by computertech.
If you don't want to go through the cleaning and drying process, I believe you can find replacement sponges (which are called, ink absorbers) online.

Best of luck!