Tom,

I ran into a similar set-up this week. The circulator (a Taco Brand Model 003) was installed on the sill cock drain of the water heater. The plumber had installed a T-fitting so that the drain could still function. This seems to be in accordance (as an option) with this document that I found at the Taco website. Hope this helps.

http://www.taco-hvac.com/uploads/Fil...ry/102-100.pdf

Eric