In most places, it"s illegal to dispose of ferric chloride, not to mention the etched copper compounds, down the sink/tub drain, toilet, etc. You"re pouring highly corrosive acid down metal pipes, somewhere along the line, and it goes into a septic system that relies on bacteria to break down the solid waste, which these chemicals will kill. Even if it were legal/organic, you risk staining any porcelain or plastic sinks, toilets, tubs, etc., especially if they have even the smallest chips, dings, scratches, cracks, etc., and wear old clothes (don"t ask me how I know such things ). If you do this, find out where you can safely dispose of the used chemicals, such as the municipal/county/state/province recycling center (sometimes operated by the local waste pickup company).
Also, submersible plastic aquarium water circulation pumps make great agitators to circulate the etchant so you don"t wind up with some areas of the board over-etched, and others under-etched. The etchant can be reused over a number of boards, BTW, but, test a drop on some scrap to see how long it will take (longer as the number of etchings increase with a given reused amount). Also, lightly (it _is_ copper) center-punch all holes before drilling for better accuracy.
It"s a very satisfying experience, though, just take precautions including eye protection, and have plenty of water nearby for inevitable goof-ups.
The best things in life aren't things ... but, a Pi comes pretty darned close!
"Education is not the filling of a pail, but the lighting of a fire." -- W.B. Yeats
In theory, theory & practice are the same - in practice, they aren't!!!