Got frustrated juggling the small glass test tubes that come with API test equipment every week, when testing water quality.
So I cut a piece of 1" thick wood, 3" x 8 " (it could be any size)
I then measured and marked where I wanted my holes to go. I took a common household drill and, using a 1/2" size Forstner bit, cut holes approx 5/8th of 1 inch deep into the wood.
My water testing Saturdays are made easier with this little piece of equipment when I check PH, NO2, NO3, Ammonia, KH & GH (in addition to temperature & salt level).