I got mine off ebay. Yes it attaches to the bottom so it will suck it back into the radiator. Drain tube goes high in the canister for the over flow and comes out the bottom as well.
They have a bunch of different sizes. I was off a little on the price..... by 2 Bucks.
I have a higher PSI Racing Cap on my radiator. Think it is 25-29PSI. I have never had even a drop leak from it.
http://www.ebay.com/itm/HOT-ROD-RAT...Parts_Accessories&hash=item41817c6060&vxp=mtr