Its all the same whether you model vessels or pumps in Caesar.As Dan suggested, model it as rigid elements with the diameters of suction & discharge sides adhering to the pump dwg (or even of larger dia{but no way lesser} than what is specified to simulate the rigid casing of pump).
The only important thing to remember is the fix point or the location for pump anchor. Do go through the pump dwg thoroughly to confirm the type of pump supporting-i mean whether its a centreline supported pump(central pedestal type) or off-centre supported or may be of some other type.
After ensuring the nozzle loads are within the acceptable limits;you also, ensure the pump & piping mating flanges are aligned within acceptable limits to avoid fututre issues at site related to pump alignment.
Don't forget to provide adjustable type of support as the first support on both the suction & discharge sides.
Hope this helps.
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Keep Smiling
SJ