Other Taxpayer is an optional parameter for revenue search. You can specify one eleven digit taxpayer ID, and TexRev will use it to filter the Taxpayer ID field opposite of the one specified in Tax Sub Type.
For example: If you selected Deep End Shale (999999999) in Target Taxpayer and the first option in Tax Sub Type, TexRev would use the Taxpayer ID value specified in Other Taxpayer to filter the purchaser IDs.