Well wadih, your friend wasn't totally wrong. Often those "pimples" you speak of are caused by a constantly moist substrate. I've seen it happen time and time again. Garter snakes seem especially prone to that problem. Overcrowding and/or constantly moist substrate will cause skin infections like you described. They look like pimples, usually on the belly, and they are filled with pus. This is why you should never use aquarium gravel or other non-absorbant substrate. Recommended substrates can be found here in the forum.

You never want to deprive garters of a source of fresh water to drink. And you always want to have a bowl of water big enough for them to curl up in and soak. However, if you can't keep the substrate dry, then your setup needs to be re-designed or re-evaluated. Even "aquatic" species of garters require no more water or moisture than terrestrial species, and ALL need to have a clean dry substrate to lie on. Even if they love to soak, they should always have a clean dry place to go when they are done with their bath.

It's clear that you may have taken the "treatment" a little too far. You're learning from the experience and that's what matters. Also you have this community of experienced garter keepers you can draw on, so stick around, and ask lots of questions, whether you think the question is stupid, or not.

Basically, like I said, you need a clean, dry surface for the snakes to live on, but they should always have the option of a good soak in the "tub" too. Glad to hear the infection cleared up. Often times, even after correcting the condition that caused the infection, it won't clear up without more aggressive treatment. In advanced cases, I resorted to scrub downs using "Hibiclens" (active ingredient Chorhexidine). Yes, I know it's poison, but it worked. The snakes I speak of were doomed to certain death if I didn't do something. They recovered. (and heck no, they weren't my snakes. I was just helping out others)

Anyway, during treatment, the snakes were kept in sterile containers, sterilized daily while the snakes were being treated with the antiseptic, and were offered the opportunity to drink twice daily.