Oh, I understand that, especially for a plumbing business owner.
I just answered the question asked.
Get your plumbing certification, a pickup truck, a phone number in the yellow pages, the tools of the trade, charge $75 an hour, and you can make about $156,000 a year (gross) in a normal working year (40 hours a week).
That's before expenses and before taxes.
work Saturday and Sunday and you can double or triple your rates
Toilets do plug and pipes do burst on weekends :-(
Better a van, harder to steal things out of. Around these parts the vehicle of choice seems to be a retired ambulance, plenty of space, storage, outdoor lighting, etc, all built in.