I would not bother trying this because there are so many good products (safe ones) out there.
Get IN the huge tub (why do builders love sticking these monsters in new homes?) Dust the outside rim, or ledge, and a foam sponge dampened with an all purpose cleaner does the job well. Then get out of the huge tub and spray on a foaming tub cleaner. IF the tub is used a lot, first remove any soap scum using whatever method works best for you. Let the cleaning solution sit a while, then rinse it off.
My other pet peeve is enormous walk in showers that do NOT have a hand held sprayer. If the shower head is on the FAR wall, to [properly rinse the shower YOU have to take a shower! This irritates me no end. Several of my customers have this situation. Luckily, they both understand the problem and do not expect me to get soaked cleaning their shower! If anyone out there has a good solution, please speak up!