After losing my vacuum cap twice, I have tethered it to my housing and never had a problem since. With both my DSLR and now mirrorless housing, I have been able so get vacuum by sucking air out my mouth. It sucks but it works!
Thanks to kallebumba, I made a handle strap and it was very easy! I felt the limited contact against the back of my hand would make it difficult to shoot one handed so I added part of an old camcorder strap and it seemed to provide more support. Now I just need to test it out underwater!
Moved over from Wetpixel. Switched from Canon 7D mark 2 to an R7 mainly for better auto focus which I now find is better at times but worst in certain situations.