Note that the commercial etchants such as the link by Pommie and this one (
https://www.jtbaker.com/msds/englishhtml/f1080.htm) have ferric chloride at a concentration of about 40% by weight. That means, 40 g of ferric chloride (anhydrous) in 100 g of solution. That is considerably more concentrated than a couple of teaspoons (assuming a density of 4, that would be about 40 g) in 250 mL or about 14% w/w. I am sure the more dilute solution will work. I am just pointing out that it is considerably less concentrated than commercial etchant and may work more slowly.
As it turns out, the commercial etchant is just a little more dilute than a saturated solution. If you buy ferric chloride as the hydrate (hexa), it will probably come in big chunks or very coarse amorphous granules. You can just add the calculated amount of water (an amount of water equal to 0.5 times the weight of ferric chloride hexahydrate will give 40% w/w) and let it sit for a few days. Gentle warming helps. Concentrated solutions are stable for a very long time.
For use, one can use the solution as is or add a little water, if you want something a little less viscous. Some sources suggest adding a little table salt (NaCl) too, which is supposed to increase the etching speed.
The difference in this procedure is starting with the hydrated salt instead of the anhydrous salt. The hydrate is usually less expensive, but most important, it does not produce the heat that the anhydrous salt does upon addition of water.
In many areas, disposal of small amounts of etchant down the drain is allowed. The hazard is not so much from the ferric chloride, but from the dissolved copper (mostly cupric).
Adding carbonate (as suggested) alkalinizes the solution and causes both iron and copper salts to precipitate. Sodium hydroxide (lye) could also be used as the hydroxides of both metals are insoluble. John