You can alternate with soapy water spray , ultra fine horticultural oil spray , BT spray and insecticidal soap spray . These products will not harm you or the water systems but will kill - on contact only - soft bodied insects like aphids , caterpillars , mites and some soft scales .
More and more commercial growers are spraying less and letting natural predators - such as parasitic wasps - do their thing with good results . Currently the biggest threat to tomatoes is thrips , silver flies , and viruses .

From an older article about homemade sprays :

" Home-made soap & oil spray for insect control
MIX: 2 1/2 TBSP cooking oil + 2 1/2 TBSP baby shampoo
Mix well in 1 gallon of water
NOTE: Shake well before and during application.
Water the plant well the day before you spray.
Do not spray during the heat of the day in full sun.
Reduce potential injury by rinsing the plant with fresh water a few
Hours after the soap spray application.
Thorough coverage of the pest is necessary so spray both sides of
The foliage thoroughly until it drips from the leaves.
Spray every 5-7 days as needed.

If a fungus is also present than add to the above formula:
2 TBSP baking soda
NOTE: Shake well before and during application.
If the weather is humid or the threat of disease is high, spray every
Five to seven days.
Spray both sides of the leaves thoroughly.
Always test any spray on a small area of the plant.
Can be used against blackspot & mildew on roses, powdery mildew
On summer squash, early blight on tomatoes and alternaria leaf
Blight on melons, and who knows what else!
(The use of soap or oil for insect control will control the insects but will do nothing to correct the condition that
is making the plant susceptible to the insects. Using foliar applications of fish emulsion and seaweed may help
ill plants do better.) "

Here is a link that might be useful: HOME REMEDIES FOR INSECT AND DISEASE CONTROL

Plant nasturtium to distract the aphids. To repel the aphids, plant strong-scented, fast to flower, allium. Alliums are things like onion, garlic, chives, etc.. But remember: if you are to do this, plant the fastest to flower kind you can find. The flowers give off the scent the aphids don't like.

I've largely been ignoring the aphids in my garden (I could spray them off but the ants are farming most of the ones on my plants and keep bringing them back) anyway, there are risks of the aphids bringing/spreading plant disease but I figure I need to let the aphids be for a while to get enough ladybugs interested in coming and helping.

So far even with my neglect, most of my plants are still managing to produce even with heavy infestations. Last season the cow peas and yardlong beans were heavily infested but I got a harvest. Same with the hot peppers and the okra.

Simply spraying with water will usually knock the aphids off and they don't usually come back right away if the ants arn't farming them. Add a little dish soap if the water doesn't do it or ignore them. But that is only my advice and I haven't had aphids attacking any tomatoes lately.

Here is a link that might be useful: TCLynx