Bloatedmostoftime
Hun, I have been doing castor oil packs for years. I have never heard of using the bathtub. But whatever works. Here is what I do & mabey you could try:
I fold like two bath sized towels in half and place one on top of the other and put them on top of my bedsheets. Then I lay down, put the oil on the flannel, apply the saran wrap & the heating pad over that. It can get on your sheets but the towels really help that from happening.
It is impossible to get the oil out of fabrics totally, in my experience. In between uses, I store the flannel in the refrigerator in a tupperware style container. Then I replace it every so often when it just feels too soaked through.
Hope that helps. Use some towels you don't mind staining. You can wash them but it will leave stains.