A bit tricky to obtain unless you're diabetic but I used a small 1ml syringe with a hypodermic needle, somewhere around a 25 gauge tip. You need a prescription however. My local clinic said they don't have any so try a pharmacy, the pharmacy clerk was verrrry reluctant to give me one, this was back when I needed one to inject earthworks with air so they'd float for trout fishing. She originally said no, but as I walked away she whispered me back and just gave me one with a wink
For vinegar and muriatic acid the small tips work really well but if you're using aptasia x you may need a larger tip as there's some sediment that will clog the tip before you have a change to get any liquid out
So either be kind and explain to your local pharmacist what you need one for (cross your fingers), or try eBay