Hi Justin,
I am not totally sure on the size, but similar to a speedster if not slightly larger.
I know I put 3 buckets in and I still had plenty of room.
As for running at 300 - 350 I dont know! I have never had to "Blast" the dirt out of a clients carpet.
I have rarely gone to 200 - 50 for both residential and domestic carpets, and probably only about 80psi on upholstery.
Lets face it, if you spill a cup of water or half a cup left for so long its at the bottom before you know it. Plus its the operaters technique and the chemicals what clean a carpet.
As for the refilling yes you are correct TMs win hands down for that. But their is a way out and I do not know who else does it. They may do my idea would be this and I have had a machine where I have done it.
I drilled a hole in the solution tank. Fitted a ball valve. Same as on the older toilets, or water tanks.
Hose connector and a hose run from customers supply either tap or outside tap. Water left on continuous, the ball valve stops the flooding as the water rises.
How about that for an idea. Even TM's have to fill up.
These days if you purchase a top quality portable, I dont mean my rhino! Theres not much difference these days between a porty & and TM.
We also find on some commercial jobs TMs are not allowed! Doors open Not allowed. Security is an issue with some commercial jobs. Even on some residential. And if you work more that 250-300 feet your losing presure - Portys still win in some cases. Plus I know I can work at 100 feet on this porty easily.
Dave