You can use a chemical de-glosser instead of sanding.Some varnishes back then had lead in them too, not just the paint. http://www.diylife.com/2010/03/08/how-to-degloss-a-surface-for-paint-prep/You need to use a contractor that is RRP certified.

I have found chemical treatment effective.

( unfortunately many tenants in america fall into this category- so i understand you but you are a landlord and you look from the landlord's perspective....want it or not), other reasons are illness, divorce, chemical adictions, loss of employment due to ****** economy, e.t.c. to name just few..........ohio is particularily affected with high unemployment rate.

Apparently the pex absorbs chemicals.

The chemical smell should be minimal once the Cover has been off for a few minutes.

Plastic just doesn't hold up long term to high pressure and the types of chemicals most of us have in our water supply.Speaking of pressure, buy yourself a $10 water pressure tester from HD, and check your water pressure every six to twelve months.

Colorado requires cleaning whereas other states allow you to use chemicals that neutralize the meth.

Beyond smell, you're going to have a reasonable amount of heavy trucks bringing chemicals, septic haulers bringing in portable crap loads, solid waste cakes being hauled to the landfill or (worse) slurry land applied. 

Water systems require backflow on commercial & multifamily because there's greater chance for someone to create the conditions that might allow a backflow scenario to exist, i.e. a hose sitting in cleaning solution, or a chemical mixer attachment on a hose, wherein a drop in pressure on the city main could cause those materials to be drawn into the distribution system.

I forget the name of the additional chemical(s), but I will make sure to look for aproduct that addresses the eggs and larva as well - not all flea foggers do,from what little I`ve been able to research in the past couple of days.