Parts Washer Solvent with Water

[gmebey]

I just picked up a 20 gal Harbor Freight parts washer and 5 gal bucket of "parts cleaning solvent", which according to the MSDS is "mineral spirits, regular" manufactured by EMCO Chemical Distributors.

To my surprise I found out that 5 gallons wasn't enough to prime the pump and at $50 a bucket I really don't want to buy another one unless I have to.

Anyway my questions are:
1) How much solvent should I expect to use for proper function?

2) What are other sources for finding solvent?

3) I have seen post on other boards about adding a couple gallons of water to allow the solvent to float on top lowing the amount of solvent required and to make a capture layer to trap dirt. Is this a good idea?

4) On one post someone mentioned that actual solvent will attack the pump. Is this true with "mineral spirits"?

Oh BTW my parts washer is outside due to limited garage space, and I tarp it to keep out rain. I live in Colorado.