Briggs and Stratton part# 291488 (6qt) and 2908016 (4qt). They both seem to cost about $65. This style won't be for everyone. It's a plain black box. For those of you who are interested, there you are. Please mount it appropriately! I'm unable to post links, but Dan was kind enough to do so- Thanks. Update: MAY-2015, I am amazed to find the price for these tanks is now $72!