Firstly, your maid did not control the amount of usage. Secondly, toilet duck is not too effective to rub off the stain marks inside the toilet bowls and she may have put more than required.
well I ask her, she says she uses BRUSH + TOILET DUCK everyday , and BLEACH two or three times a week (umm, maybe she thinks my toilets are very dirty?!?!?!)
actually at first when i ask her why she used 3 bottles within 1 month, she tell me I only bought 2 last time. But later I check, confirm bought 3 ga! So I ask her, she just say "yes because I clean the toilet everyday, so finish quickly" ..
ai, don't know if she really use it (waste too much), or lying - but, if she is lying, what did she do? sell it?! "ng hai gua..!!!!"