I am sorry Diesel is unwell. This is quite a common problem and shouldn't be too much of an issue. However, persistent vomiting, anorexia and absent drinking will require him to be seen by your vet as dehydration would be a concern as well as the possibility of an impaction if a large amount of sand has been consumed.
It is likely the sand is irritating his stomach, so I would starve him for 24 hours and then offer a bland highly digestible diet
However, water should remain freely available but I would offer this in small quantities, maybe with a teaspoon of sugar in it. Small frequent amount avoid it being vomited straight back.
Following the starvation period a bland, highly digestible diet should be fed. For more details on what to feed see below. This can assist with gastrointestinal recovery. This should initially be in small frequent meals, usually 6-8 small meals are recommended on the first day. If vomiting recurs/persists then your pet should be examined. Diarrhoea will take a few days to settle so an instant improvement is not always seen. If your pet remains happy and alert and is eating well then over the next 2-3 days the meal size should increase and the frequency decrease. Once meal size is normal and frequency is normal then the usual diet should be SLOWLY re-introduced. Take 3-5 days to transition from the bland food to the normal diet.
Your pet should be re-examined if diarrhoea persist or clinical signs recur. Proteins include chicken (boiled, no skin or bones) turkey, white fish, scrambled eggs (made with water not milk) or low fat cottage cheese. Carbohydrates include rice, mashed potatoe, sweet potatoe and pumpkin.
You should select one food type from the protein list and one from the carbohydrate. If you have any worries, questions or concerns or if your pet is developing worse clinical signs then contact your vet.
You should also try giving him some ranitidine (Zantac) this calms the stomach juices, reduces acidity and can help with vomiting. Provide him with 1ml per 5kg body weight twice a day for 3-5 days (as long as he is getting better).
BUT if he is not getting better or getting worse, he should be seen by your vet.