First off slavery was abolished over 125 years ago, and having them perform roadwork, trash removal or urban beautification projects would be cutting jobs that traditionally are done by paid union employees. Further more you would be opening the state up to multi million dollar lawsuits when the truly lazy get hurt the first 15 minutes that you are trying to get your pound of flesh.
As for the drug testing how often are they tested, and who foots that bill? I don’t think you have anymore right to drug test people on welfare anymore then I do to sell them a hunting license or as part of a loan application.
I don't see how slavery was even brought into this discussion. The people receiving benefits would be working for there assistance check. Slavery is a form of forced labor in which people are considered to be, or treated as, the property of others. Slavery and working to get public assistance, no connection between the two.
Performing road work should be left to PennDot and such but, trash removal and beautification projects are mostly done by volunteers. So I can't see your argument of loss of union jobs on that one.
As for who will pay for the test. The PA Department of Corrections drug test every inmate in the state at least every 6 months already. I'm sure the state can get an even better contract with the drug testing companies if this plan was involved also. I went onto PA assistance web site to get some $$ examples. From what I can tell from the site a single person getting assistance gets about $500 a month with food stamps and cash assistance plus FULL MEDICAL COVERAGE. As we all know what a doctor's visit can cost. You could go even deeper into it and look at all the low income housing and the limiting on how much people on public assistance pay for utilities. All payed by our tax $$$. From looking at that I believe it will more than pay for itself.