How to say “tastes bad” for inedibles?
味道不好的牙膏 ？

Yes, 味道不好 or 味道很差  would do
味道不好 (doesn't taste good) e.g. 这漱口水味道不好，像消毒酒精一般的
味道很差 (taste awful) e.g. 这口香糖味道很差，像咳嗽药水一般的
这牙膏味道不好/很差，薄荷味太重
Also: 難以入口 (too awful to put in mouth)
Example:
嚼烟草对不吸烟的人来说是难以入口的
这有苦味的口香糖真是难以入口
这有重酒精味，难以入口的漱口水也拿出来卖？
imrek wrote:

X(的)味道很难受: X tastes bad

Yes, you can substitute 不好(not good) or 很差(very bad) with 很难受 (hard to take) in the first three examples I provided
Beside 漱口水，口香糖，牙膏， 嚼烟草 and 檳榔 , I can't think of anything else with a taste that you put in the mouth but not supposed to swallow it