Attached are three pics of my plastic water block. This was
made from a 4″ PVC cap made for sewer clean-outs. They cost less than $2 at the local hardware store.
It turns out that the hollow space inside the square knob
measures 39mm by 39mm, perfect for mounting a standard 40mm peltier. I cut away the extraneous portions of the cap, leaving just enough for some bolt holes.
I sanded it flat and left it a little rough (for a better bond).
Then I glued the peltier in place with some JB Weld. This set up directly water cools the hot side of the pelt.
The picture below shows the rig mounted on my slot 1 Celeron (soon to be replaced by my new Celeron II).
BTW: This is the PVC cap in its “natural environment”: