Not just the Peter's Pence, but each church must give a percentage of everything they receive (collections, wills, lump sum donations) to the local Bishop.
Does the SSPX?
And just a thought while we're on the subject of SSPX and money.
I've never seen a poor box in an SSPX chapel or a St. Vincent De Paul society
or a Right to Life. Do they ever help anyone other than themselves?