The gravel vac/siphons I've seen are too big for tanks smaller than 5gal, in my opinion. More money than I want to spend, too. Four tanks need four siphons, and they all eventually need cleaning.
Following Old Fish Lady's lead, I make these for fifty-cents apiece. I don't count the R&D time and expense.
The tubing is 1/2in dia x 6ft long ($0.08/ft neoprene from the hardware store).
The pill bottle is 1in dia ($0.00).
The stick is from a plastic clothes hanger ($0.00) OFL uses chopsticks. Anything non-metallic will do.
I've had success with clear strapping tap or medicinal paper tape. I'm sure anything will work. ($0.00)
Cut (drill,melt) the 1/2dia hole for a snug fit for the tubing. It doesn't have to be perfect; no sealant is necessary. Putting it near the edge makes it easier to build and to use.
Stick the tube in about 1/4in. Twist-tie or tape near the top of the stick.
This combination, in my experience, is strong enough to suck up debris without removing gravel, disturbing plants or endangering fish.
Total cost< 50 cents