my advice is to go buy a slide bowl for a bong from a head shop. it'll be like 5-10$, and i hate to say this, but unless you already have one, you need it. just melt a hole in the cap, slide the bowl stem into the hole (use a rubber O ring if you can get one from the head shop) and you are good to go.

also, if you have to use tin foil, you shouldnt be smoking weed, go get a job.