how long does a normal propane tank last you?

I use two 20# tanks, as I run two burners at once at some points in my process. I generally get through two to three ten-gallon batches, using the burners to heat everything. This does not run the tanks dry, but makes them light enough that I get hinky and run them over to the rental place for a refill.

They charge by the gallon pumped, and usually round down - "All right, I filled five point two gallons, I'll call it five gallons and have a nice day!" I really need to take those guys a sixer one of these days.

quite a setup in the basement - and I DO like the constant temp, no bugs etc..

I have a semi-finished room in my basement which I have thought of converting ...sinks etc ... and there IS a window to the outside ..

HMMMM - maybe Mr Bush's check will pay a plumber and buy some sinks !