Doesn't matter what type. But as long as you're just going to use plastic bottles, might as well use another one as a bc. I think I used a small Gatorade bottle way back. Small bottle, with a big cap so I could drill two holes for tubing into.
If you want to get fancy, there are bubble counters out there that have compression fittings at both ends. Unnecessary and more costly than a plastic bottle, but to each his own.