Usually in a level. the liquid in the little glass tube with the bubble is only water, but sometimes it is oil. They are often also used as a measuring tool.
- L1 levels are usually a little sticky if she handles it immediately after she gives you a hand job.
- L2 levels are always clean if she swallows.
- The bubble in L3 levels breaks up into lots of small ones if the massage table shakes too much while fucking the masseuse.
If you allow her use a disposable tape or string to measure your junk, she wont have to worry about cleaning it up every time.