Configuring UTM to provide two subnets on one port connection using vlans.

To date I have created subnets on my UTM with ports connected to a managed switch.  All the heavy lifting such as dhcp, dns etc is done by the UTM which connect to access ports for each subnet on the switch.   All the vlan work to manage the subnets is then done on the switch. 

I have 5 available ports on the UTM and now need six subnets and so I run out of ports on the UTM.  I need to connect six subnets to 5 ports. 

I think what I want to do is create two vlans on the UTM and assign the two subnets to these vlans with dhcp and dns associated.  What I am not sure about is how to get the traffic through the one port and land it on the switch.   Please could I have some help doing this on the UTM and how to deal with tagged traffic from UTM on the switch.